PI3KC3/BECLIN1-dependent lipophagy mediates phosphorus-induced reduction of hepatic lipid deposition in hybrid yellow catfish.

To investigate the molecular mechanism by which phosphorus (Pi) regulates hepatic lipid deposition in hybrid yellow catfish (Pelteobagrus fulvidraco × Pelteobagrus vachelli), a 56-day in vivo feeding trial was conducted with five dietary Pi levels: 0.54%, 0.65%, 0.74%, 0.98%, and 1.28%. Combined with in vitro incubation experiments using primary hepatocytes, this study focused on the PI3KC3/BECLIN1-mediated lipophagy pathway to assess hepatic morphology, expression of autophagy-related genes/proteins, and lipophagic activity. The results showed that hepatic morphology was intact in fish fed 0.65%-0.74% dietary Pi, whereas obvious vacuolization and lipid accumulation were observed in the 0.54% and 1.28% Pi groups. Pi levels of 0.74%-0.98% activated hepatic lipophagy and significantly upregulated the mRNA and protein expression of autophagy-related markers including PI3KC3, BECLIN1, and LC3B-II. In vitro experiments revealed that 2 mM Pi supplementation markedly reduced triglyceride (TG) content in oleic acid-induced hyperlipidemic hepatocytes, enhanced the protein expression of SLC20A1 and SLC20A2, promoted the physical interaction between PI3KC3 and BECLIN1, and strengthened lipid droplet-lysosome colocalization. These effects were significantly suppressed by the autophagy inhibitor 3-MA. In addition, Pi upregulated the expression of the hepatocellular Pi transporters SLC20A1 and SLC20A2 and induced a transient increase in intracellular free calcium ions. This study proposes a potential mechanism whereby Pi may initiate autophagy by promoting the binding of PI3KC3 to BECLIN1, thereby enhancing hepatic lipophagy and alleviating lipid deposition. These findings provide potential novel targets for the nutritional prevention and control of fatty liver disease in yellow catfish.